Cycles special Water shader (Low Poly)
Ground surface have to keep own relief under water surface;
In original picture probably presents some specific HDR environment map producing specific light, hard to achieve with common light sources.
I'm not shure you need decimate modifier (but this not really important).


Well. I tried to reproduce original picture (but without HDR environment). Afraid it will took much longer time to write what I've done than time I had spent doing this scene :)